I did use Userpro but my blog suffered from low visitors and never allowed to fully test its potential. I averaged about 500 visitors a day and was only able to get 15 users signed up to the forums each month - So had to shut down the forums altogether.
As far as Userpro is concerned - its quite good. works very well with almost all major theme frameworks and just needs a little tweaking here and there to set it right (use the help of documentation provided)
I first turned on all the features, which I later realized to be only mere gimmicks because my wasn't a fully blownup forum. So turned off many features but left only the major ones. It's Social features are good and does seem to work very well, but as I said, I never many users to put them to a good test.
So, as far as functionality is concerned, its quite good. Get a good number of users to sign up and slowly unleash the features to keep your users engaged - use trial and error for optimal results - Userpro has tons of features to let you do all that.